1. Field of the Invention
The present invention relates to a battery assembly, which can be used suitably as an electric power source for electric vehicles and hybrid vehicles.
2. Description of the Related Art
Nickel-hydrogen secondary battery and lithium ion battery, which are used as an electric power source for driving electric automobile, have been required to exhibit a high energy density, and have been demanded to occupy least on-board space as much as possible. Accordingly, it has been a general practice to make a battery assembly by assembling a plurality of single-battery cells. For example, a few dozens of single-battery cells, which are formed as a rectangular parallelepiped configuration and whose battery capacity is from a few volts to a few dozens of volts, are connected in series, and then the resulting battery subassembly is stored in a package to make a battery assembly. The resultant battery assembly has been installed under the rear passenger seat of vehicle or in the trunk room thereof, for instance.
However, the performance and longevity of battery assembly depend greatly on temperature conditions, that is, the higher the ambient temperature is the more likely it is that the performance and longevity have degraded remarkably. In view of this, it has been carried out to form a cooling passage, which communicates with the atmosphere, on the surface of single-cell battery; and then to introduce the passenger-room indoor air into the resultant cooling passage, or to forcibly introduce the air-conditioning air into it.
Meanwhile, in nickel-hydrogen secondary battery, for instance, it is impossible to avoid such a phenomenon that the single-battery cells, which are formed as a rectangular parallelepiped configuration, expand upon charging the nickel-hydrogen secondary battery so that the single-battery cells' largest-area side surfaces bulge outward like an arc shape. If such is the case, in a battery assembly which is made up of a plurality of assembled single-battery cells that are formed as a rectangular parallelepiped configuration, it is probable that a large stress might concentrate on the contacted site because the single-battery cells' opposite wall surfaces, their opposite largest-area side surfaces, contact with each other in a small contact area.
Accordingly, for the purpose of making the charging/discharging characteristics of respective single-battery cells uniform by means of equalizing the inner pressures of respective single-battery cells, it has been carried out to apply a predetermined load to a plurality of single-battery cells, thereby arranging the single-battery cells in such a manner that they are pressurized to be bound to each other. For example, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2001-313,018 discloses such a battery assembly. In this conventional battery assembly, a plurality of single-battery cells are arranged in the thickness direction, a binder plate is superimposed on the thickness-wise opposite ends, respectively; and then the two binder plates are tightened up with a clamping rod in such a direction that they approach to each other. Consequently, it is possible to adhere the single-battery cells to each other, because the two binder plates are tightened up in such a direction that they approach to each other. Thus, loading a predetermined load to the respective single-battery cells makes it possible to inhibit them from expanding as described above.
However, the conventional battery assembly set forth in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2001-313,018 is associated with such a problem the single-battery cells, which are disposed at around the central portion, are less likely to radiate heat than the single-battery cells, which are disposed at around the opposite ends, do. When the respective single-battery cells thus exhibit differing cooling characteristics to each other, fluctuations, such as fluctuating outputs and fluctuating longevities, have occurred between the respective single-battery cells. As a result, the conventional battery assembly has come to output electricity unstably, and has eventually come to show a shortened longevity.
In view of above, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2007-12,486 proposes a battery assembly in which the tops of a plurality of single-battery cells are accommodated in a battery chamber with a sealed construction; and in which the bottoms of the respective single-battery cells are exposed out into a cooling chamber. The conventional battery assembly makes it possible to cool the respective single-battery cells uniformly by distributing a cooling medium, such as cooling air, through the cooling chamber.
Moreover, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 7-45,310 proposes a battery assembly, which comprises a plurality of heat pipes, a plurality of single-battery cells, and a plurality of radiator plates. The heat pipes are disposed near the single-battery cells, respectively, and the ends of the heat pipes are engaged with the radiator plates. Thus, the heat, which is produced in the single-battery cells, is radiated to the outside.
However, the above-described conventional battery assemblies have been jumboized or grown in size because they have complicated structures. Therefore, they suffer from a drawback in view of on-board space, or in view of cost.
Taking the aforementioned problems into account, the following practice has been carried out, for example, as set forth in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2006-48,996. Specifically, as illustrated in FIG. 12, a spacer 101 is interposed between two paired single-battery cells 100, 100; a plurality of the resulting battery subassemblies are disposed one after another in a row so that the paired single-battery cells 100, 100 and the spacers 101 are disposed alternately so as to face the largest-area side surfaces of the paired single-cell battery cells 100, 100 to each other by way of the spacer 101 intervening therebetween; a binder plate 102 is disposed at the opposite ends of the resultant battery subassembly, respectively; and the binder plates 102, 102 are bound with a clamping rod in the direction of disposing the battery subassemblies one after another, thereby completing a battery assembly. In the conventional battery assembly, the spacers 101 are provided with ribs 103, thereby forming a space 104, which exhibits a height of from 1 to 2 mm, between each of the single-battery cells 100 and spacers 101, respectively. Therefore, even when the single-battery cells 100 expand, it is possible to prevent the facing wall surfaces of the single-battery cells 100, the facing largest-area side surfaces thereof, from interfering with each other. Moreover, it is possible to cool the single-battery cells 100 by flowing a cooling medium, such as air, through the spaces 104. Thus, it is possible to make the cooling characteristic, which is likely to fluctuate between the singe-battery cells 100, uniform, and thereby it is possible to extend the longevity of the respective single-battery cells 100.
However, in the conventional battery assembly that is set forth in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2006-48,996, there might occur such an instance that foreign materials, such as dust, deposit in the spaces 104 of the battery subassemblies. If such is the case, it becomes difficult to cool the respective single-battery cells 100 uniformly so that differences have arisen between the cooling characteristics that the single-battery cells 100 exhibit. Moreover, although air from air conditioner has been used in general as cooling medium, the air might result in dew condensation in the spaces 100 depending on the temperature difference between the air and the outside air. If the resulting dew drops should have moved to the electrodes of the single-battery cells 100, it is not necessarily possible to say that the conventional battery assembly could have hardly been short-circuited.